Filter paper

ABSTRACT

This instant invention relates to a filter paper suitable for use at an elevated temperature using an adhesive composition comprising a heat curable water-based polyvinyl acetate thermosetting resin adhesives comprising, in addition to the resins noted, water-soluble methyl cellulose in an amount sufficient to form a non-elastic continuous film on the adhesive surface when exposed to curing temperatures.

United States Patent Columbus et al.

[54] FILTER PAPER [72] Inventors: Peter S. Columbus, Whitestone,

N.Y.; Carl R. Erikson, Maywood,

[73] Assignee: Borden, Inc., New York, NY.

[22] Filed: Nov. 18, 1970 [21] Appl. No.: 90,848

Related US. Application Data [62] Division of Ser. No. 698,705, Jan. 18, 1968,

Pat. No. 3,542,706.

[52] US. Cl. ..2l0/493 [51] Int. Cl. ..B0ld 29/06 [58] Field of Search ..1 17/161 165; 260/15; 210/493 [56] References Cited UNITED STATES PATENTS 2,739,916 3/1956 Parker ..2l0/493 [151 3,692,185 [45;] Sept. 19, 1972 2,726,184 12/1955 Cox et al. ..210/493 2,633,660 12/1953 Layte ..2 10/493 3,042,571 7/1962 Jackson ..2l0/493 Primary Examiner-Samih N. Zaharna Assistant Examiner-Frederick F. Calvetti Attorney-John L. Sigalos [5 7] ABSTRACT 3 Claims, No Drawings FILTER PAPER CROSS REFERENCE TO RELATED APPLICATIONS This application is a divisional application of Ser. No. 698,705, filed Jan. 18, I968, now U.S. Pat. No. 3,542,706.

BACKGROUND OF THE INVENTION At the present time adhesives are used in which the resinous components are polyvinyl acetate and thermosetting resins. While satisfactory for most uses, it has been found that when subjected to elevated temperature as at about 350500F., as in the preparation of oil filters when filter paper is adhered to other sub strates, such adhesives bubble and splatter the filter paper making the adhesive unsuitablefo'r this use. In addition, the adhesive channels along the fluted filtered paper stock of the filter sealing this porous area and negating its filtering function. This channeling and bubbling by decreasing the amount of adhesive at the bonding area leaves a weak and non-continuous cured adhesive film between the paper stock and the metal, such as steel or tin, plate adhered to the paper in making the enclosed filter.

Attempts have been made in the past to overcome this bubbling by speeding up the curing rate of the resins in order to have an extremely rigid surface film at the earliest possible time to prevent bubbling. Such products do not work satisfactorily since the materials used to increase the curing rate give the product a relatively poor stability and short shelf life.

SUMMARY OFTI-IE INVENTION The present invention provides an adhesive composition which is substantially non-bubbling at the elevated temperatures noted and in which the thin continuous surface film first formed upon heating to cure is substantially nonelastic; the film cracks to permit escape of volatiles which would otherwise exert pressure underneath the film and cause bubbling with the ill effects set forth above.

Briefly stated, the present invention comprises an adhesive that is substantially non-bubbling when cured at elevated temperatures (above 212F.) comprising a polyvinyl acetate, a thermosetting resin cross-linkable with said polyvinyl acetate resin, and water'soluble methyl cellulose in an amount sufficient to form a nonelastic continuous film on the adhesive surface when exposed to curing temperatures.

DETAILED DESCRIPTION As to materials, the polyvinyl acetate used can be any homopolymer or copolymer latex or emulsion commonly used in making adhesives as more particularly described in US. Pat. Nos. 2,902,458 and 2,902,459; and for best results a combination of medium and high molecular weight acetate resins in the proportion of about 1 to about 2 parts by weight of medium molecular weight acetate for each part by weight of high molecular weight acetate. The terms medium and high" molecular weight are meant to denote a range of molecular weight as understood in vinyl acetate polymerization art. Thus, medium molecular weight is from about 30,000 to about 80,000 and high anything over about 100,000.

The thermosetting resin used can be any curable compound cross-linkable with the polyvinyl acetate. Preferred are phenol-formaldehyde resoles. Also operative are urea-formaldehyde, phenol-formaldehyde novalaks, and the like phenolic-aldehyde and urea-aldehyde resins. Suitable examples are also set forth in U.S. Pat. No. 2,902,459.

It is to be pointed out that the polyvinyl acetate and thermosetting resins used and proportions thereof are those commonly used and well-known in the art e.g., the weight ratio of polyvinyl acetate resin to thermosetting resin being in the range of 1:1 to 1:5 as dis closed in US. Pat. No. 2,902,459.

The water-soluble methyl cellulose is the critical component of the composition. Attempts to use other water-soluble materials have proven unsuccessful. Thus, carboxymethyl cellulose, hydroxyethyl cellulose, polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene oxide, polyacrylates, polyvinyl methyl ether, and polyvinyl methyl ether/maleic anhydride are not suitable.

The methyl cellulose preferred is one having a methoxyl content of from about 26 percent to about 33 percent.

The methyl cellulose is unique. ltpermits a gelling of the wet adhesive when subject to curing temperature thus resulting in a surface film on the adhesive which cracks to let the volatiles escape through fissures. There is no spattering of the adhesive over the fluted filter paper as is the case with the elastic film of the prior art adhesives when ruptured.

The proportion of methyl cellulose used is important. In particular, the methyl cellulose must be present in such proportion that the film first formed when the adhesive is exposed to elevated temperatures for curing will be non-elastic film; Le, a proportion of 0.1 6 parts by weight of methyl cellulose for parts by weight of polyvinyl acetate solids and preferably 0.5 l part by weight.

The invention will be further described in connection with the following examples which are set forth for the purpose of illustration only and wherein proportions are in parts by weight unless specifically stated to the contrary.

EXAMPLE I Two adhesives were prepared having the following formulations:

Total: 10010 Polyco 1 I785 Polyco I88 Combination of Antifoam AF-66 silcone emulsion and Colloid No.

581 10% Al Stearate in 3 parts polyoxyethylene and 1 part ll-l3 paraffin Both adhesives were separately tested by being placed in a 50 mm. aluminum weighing dish to a depth of three-sixteenths inch. A section of pleated filter paper was placed in the adhesive so that the paper was touching the bottom of the dish. The dish was then placed on a hot plate at 375F. for minutes until the adhesive cured. The dish was then removed from the hot plate and cooled to ambient temperature. The dish was examined for bubbling and channeling during heating and after cooling.

As to adhesive A, during heating numerous bubbles formed and broke splattering adhesive over the pleated filter paper. In addition, the filter paper was seen to absorb the adhesive splattering thereon. After curing and cooling it was noted that areas of the filter paper as high as 1 inch above the surface of the original adhesive level of three-sixteenths inch were covered with a coat: ing of cured adhesive film. Also, many areas of the filter paper above 1 inch were covered with spots of cured adhesive caused by the splattering.

With adhesive B, no bubbling or spattering occurred during heating nor was any channeling noted. After curing and cooling the dish was examined and it was found that, at most, areas of the filter paper one-sixteenth inch above the surface of the original adhesive level of three-sixteenths inch were covered with a coating of cured adhesive film.

EXAMPLE 2 A series of adhesives of the following formulations were prepared;

The adhesives were each tested as set forth in Example l and in each case no bubbling occurred.

EXAMPLE 3 A series of adhesives are made using the identical formulation set forth in Example 2 except that the polyvinyl acetate homopoly'mers and copolymers disclosed in US. Pat. Nos. 2,902,458 and 2,902,459 are each separately and in turn, substituted in equal proportions by weight for the polyvinyl acetate disclosed in adhesive A therein. In each instance a non-bubbling adhesive is obtained.

While the precise theory is not understood, it is believed that at the elevated temperatures (up to about 550F.) used the thin layer of adhesive film first formed includes gel areas in the continuous film. These areas are non-elastic in nature and tend to break or fracture rather than expand thus allowing the volatiles such as water vapor and gas to escape. Heretofore, the use of polyvinyl acetate-phenolic resins for the same purpose resulted in surface layers which before they were fully cured, were still thermoplastic in nature and expande like rubber. It was the rupturing of these rubbery expansions that caused the bubbling and splattering and channeling referred to above.

It will be understood that it is intended to cover all changes and modifications of the Examples of the invention herein chosen for the purpose of illustration which do not constitute departures from the spirit and scope of the invention.

What is claimed is:

I. A filter element comprising a fluted filter paper adhered at both ends to a metal substrate with an adhesive composition consisting essentially of an aqueous dispersion of polyvinyl acetate resin, a thermosetting resin cross-linkable with polyvinyl acetate resin selected from the group consisting of phenolaldehyde condensation products and amino compound-aldehyde condensation products, and water soluble methyl cellulose in the proportion of about 0.1 to about 6 parts by weight for parts by weight of polyvinyl acetate solids, the weight ratio of polyvinyl acetate resin to thermosetting resin being in the range of 1:1 to 1:5, said adhesive being in cured condition.

2. The filter of claim 1, wherein the filter is an oil filter, the paper is fluted and adhered at both ends to an oil impervious plate.

3. The filter of claim 2 wherein the methyl cellulose has a methoxyl content of from about 26 percent to about 33 percent and is present in the proportion of about 0.5 to 1 part by weight. 

2. The filter of claim 1, wherein the filter is an oil filter, the paper is fluted and adhered at both ends to an oil impervious plate.
 3. The filter of claim 2 wherein the methyl cellulose has a methoxyl content of from about 26 percent to about 33 percent and is present in the proportion of about 0.5 to 1 part by weight. 